Image display apparatus

ABSTRACT

An image display apparatus includes an image forming device having pixels; a collimating optical system collimating light from the image forming device; and an optical device receiving, guiding, and outputting the collimated light as directional rays in different directions. The optical device includes a light-guiding plate; a first optical member reflecting or diffracting the light so as to totally reflect the light inside the light-guiding plate; and a second optical member causing the propagated light to emerge from the light-guiding plate. When a light ray emitted from a pixel located farthest from the center of the image forming device and a light ray emitted from a pixel located at the center of the image forming device pass through a front nodal point of the collimating optical system and are respectively incident on the collimating optical system and the light-guiding plate at angles θ 1  and θ 2 , θ 2 &gt;θ 1  is satisfied.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/254,981 filed Oct. 21, 2008, which claims priority to Japanese PatentApplication JP 2007-309045 filed on Nov. 29, 2007, the entire contentsof which are incorporated herein by reference.

BACKGROUND

The present application relates to image display apparatuses used forenabling an observer to observe a two-dimensional image formed by animage forming device or the like.

There are some virtual image display apparatuses (image displayapparatuses) each enabling an observer to observe a two-dimensionalimage formed by an image forming device in a form of a virtual imageenlarged by a virtual optical system, as disclosed in JapaneseUnexamined Patent Application Publication (Translation of PCTApplication) No. 2005-521099 and Japanese Unexamined Patent ApplicationPublication No. 2006-162767, for example.

FIG. 11 shows a conceptual diagram of an exemplary image displayapparatus 410. The image display apparatus 410 includes an image formingdevice 411 having a plurality of pixels arranged in a two-dimensionalmatrix, a collimating optical system 412 collimating light emitted fromthe pixels of the image forming device 411, and an optical device 20receiving the light collimated by the collimating optical system 412into a plurality of directional rays traveling in different directions,guiding the light therethrough, and outputting the light. The opticaldevice 20 includes a light-guiding plate 21 propagating thereinside thelight received thereby with total reflection and outputting thepropagated light, a first optical member 30 (a layer of reflective film,for example) reflecting the light received by the light-guiding plate 21so as to cause the light received by the light-guiding plate 21 to betotally reflected inside the light-guiding plate 21, and a secondoptical member 40 (a multilayer reflective film, for example, in which anumber of films are stacked) causing the light propagated with totalreflection inside the light-guiding plate 21 to emerge from thelight-guiding plate 21. Apparatuses, such as head-mounted displays(HMDs), that includes the image display apparatus 410 having theabove-described configuration can be made lighter and smaller.

SUMMARY

The image display apparatus 410 of the related art is designed such thatcenter light ray CL emitted from the center of the image forming device411 and passing through a nodal points of the collimating optical system412 near to the image forming device 411 (hereinafter also referred toas the “front nodal point”) perpendicularly strikes the light-guidingplate 21, that is, the center light ray CL emitted from the center ofthe image forming device 411 and passing through the front nodal pointof the collimating optical system 412 is incident on the light-guidingplate 21 at zero degrees. Although an antireflective film (not shown) isprovided on the plane of incidence of the light-guiding plate 21,referring to a conceptual diagram shown in FIG. 12, part of the light(denoted as A in FIG. 12, for example) incident on the light-guidingplate 21 may be reflected (as denoted by B in FIG. 12) at the plane ofincidence of the light-guiding plate 21 and may be fed back to thecollimating optical system 412 and further to the image forming device411.

Let us assume that the right part of the image forming device 411 shownin FIG. 12 displays a “white” image and the left part displays a “black”image. In this case, part of the “white” image may be reflected at theplane of incidence of the light-guiding plate 21 and may be incident onthe left part of the image forming device 411 displaying the “black”image. Such a phenomenon may ultimately result in a reduction in imagecontrast. More specifically, let us assume that the right part of theimage forming device 411 displays an image with a light quantity of 100,for example, and the left part displays an image with a light quantityof 4, for example. If the image displayed on the right part of the imageforming device 411 is reflected by at plane of incidence of thelight-guiding plate 21 and an image with a light quantity of 0.4 is fedback to the image forming device 411, a kind of ghost image with a lightquantity of 0.4 appears on the left part of the image forming device411. The brightness of the ghost image is equivalent to 10% of the lightquantity of 4 of the image that should be displayed.

In light of the above, it is desirable to provide an image displayapparatus in which none of the light that is emitted from an imageforming device, is transmitted through a collimating optical system, andis incident on a light-guiding plate is fed back to the image formingdevice.

According to a first or second embodiment of the present application,there is provided an image display apparatus including the followingelements:

(A) an image forming device having a plurality of pixels arranged in atwo-dimensional matrix;

(B) a collimating optical system collimating light emitted from thepixels of the image forming device; and

(C) an optical device receiving the light collimated by the collimatingoptical system into a plurality of directional rays in differenttraveling directions, guiding the light therethrough, and outputting thelight,

where, the optical device includes the following elements:

(a) a light-guiding plate propagating thereinside the light receivedthereby with total reflection and outputting the propagated light;

(b) a first optical member reflecting or diffracting the light receivedby the light-guiding plate so as to cause the light received by thelight-guiding plate to be totally reflected inside the light-guidingplate; and

(c) a second optical member causing the light propagated with totalreflection inside the light-guiding plate to emerge from thelight-guiding plate.

In the image display apparatus according to the first embodiment, whenthe light emitted from a pixel located farthest from the center of theimage forming device and passing through a nodal point of thecollimating optical system near to the image forming device (the frontnodal point) is incident on the collimating optical system at an angleof θ₁, and when the light emitted from a pixel located at the center ofthe image forming device and passing through the nodal point of thecollimating optical system near to the image forming device (the frontnodal point) is incident on the light-guiding plate at an angle of θ₂, acondition of θ₂>θ₁ is satisfied.

Further, an optical baseline optically extending through the center ofthe image forming device and the front nodal point of the collimatingoptical system is not parallel to a normal to the light-guiding plate atthe intersection of the optical baseline and the plane of incidence ofthe light-guiding plate. Therefore, the light emitted from a pixellocated farthest from the center of the image forming device, passingthrough the collimating optical system, and striking the light-guidingplate is reflected by the light-guiding plate in a direction away fromthe image forming device.

In the image display apparatus according to the second embodiment, thelight emitted from every pixel of the image forming device andcollimated by the collimating optical system into a directional rayincident on the light-guiding plate is obliquely angled with respect toa normal to the plane of incidence of the light-guiding plate.

Further, in the image display apparatus according to the secondembodiment, it is preferable that the light emitted from every pixel ofthe image forming device and collimated by the collimating opticalsystem into a directional ray have a portion thereof reflected, if any,at the plane of incidence of the light-guiding plate in a direction awayfrom the image forming device.

As a matter of convenience, the image display apparatus according to thefirst or second embodiment including the preferable configurationdescribed above (hereinafter also generally referred to as simply “theimage display apparatus of the present application”) will be describedon the basis of the following denotations: a normal to the plane ofincidence of the light-guiding plate that extends through the origindefined at the center of the first optical member and takes positivevalues in a direction toward the collimating optical system is denotedas an X_(i) axis, an axis of the light-guiding plate that extendsthrough the origin while being orthogonal to the X_(i) axis and takespositive values in a direction toward the second optical member isdenoted as a Y_(i) axis, a light ray that is emitted from a pixellocated farthest from the center of the image forming device and near tothe second optical member and passes through the front nodal point ofthe collimating optical system is denoted as a “near-end-pixel ray”, alight ray that is emitted from a pixel located farthest from the centerof the image forming device and away from the second optical member andpasses through the front nodal point of the collimating optical systemis denoted as a “far-end-pixel ray”, and a light ray that is emittedfrom the pixel located at the center of the image forming device andpasses through the front nodal point of the collimating optical systemis denoted as a “center light ray”.

In the image display apparatus according to the first embodiment, it canalso be said that the angle formed between the Y_(i) axis or an axisparallel to the Y_(i) axis and the near-end-pixel ray or thefar-end-pixel ray is an acute angle, or that the angle formed betweenthe Y_(i) axis or an axis parallel to the Y_(i) axis and thefar-end-pixel ray or the near-end-pixel ray is an obtuse angle. On theother hand, in the image display apparatus according to the secondembodiment, it can also be said that the center light ray is opticallyparallel to or not optically parallel to an X_(i)Y_(i) plane while beingacutely or obtusely intersects with an X_(i)Z_(i) plane. That is, thecenter light ray is incident on the light-guiding plate at an (acute)angle from a side near to the second optical member or at an (obtuse)angle from a side away from the second optical member.

The image display apparatus according to the first embodiment may beconfigured in such a manner that the light ray emitted from a pixellocated farthest along an axis corresponding to the Y_(i) axis from thecenter of the image forming device and passing through the front nodalpoint of the collimating optical system is incident on the collimatingoptical system at an angle of θ₁.

In the image display apparatus of an embodiment, the optical axis of thecollimating optical system may optically extend through the center ofthe image forming device. In this case, the optical axis of thecollimating optical system coincides with the optical baseline. In somecases, the center of the image forming device may or may not lie on theextension of the optical axis of the collimating optical system. In thecase where the center of the image forming device does not lie on theextension of the optical axis of the collimating optical system, thecollimating optical system can be configured in such a manner that theoptical axis thereof extends through the center of the image formingdevice via other optical systems. For this reason, it is described thatthe optical axis of the collimating optical system “optically” extendsthrough the center of the image forming device. This also applies to theother parts in the specification. Further, in the image displayapparatus of the present application, the optical axis of thecollimating optical system may be parallel to a normal to a plane ofincidence of the light-guiding plate, the normal extending through thecenter of the first optical member, while the optical axis of thecollimating optical system may optically extend through a point awayfrom the center of the image forming device.

There are several image forming devices suitable for the image displayapparatus of the present application including the preferableconfigurations described above, such as an image forming deviceincluding a reflective spatial light modulator and a light source; animage forming device including a transmissive spatial light modulatorand a light source; and an image forming device including light-emittingelements such as organic electroluminescence (EL) elements, inorganic ELelements, and light-emitting diodes (LEDs). In particular, it ispreferable that the image forming device include a reflective spatiallight modulator and a light source. Exemplary spatial light modulatorsinclude a light valve, such as a transmissive liquid crystal display ora reflective liquid crystal display employing a technique ofliquid-crystal-on-silicon (LCOS), and a digital micromirror device(DMD). Exemplary light sources include a light-emitting element.Further, the reflective spatial light modulator may include a liquidcrystal display and a polarization beam splitter, the polarization beamsplitter reflecting part of light emitted from the light source andguiding the part of light to the liquid crystal display whiletransmitting part of light reflected by the liquid crystal display andguiding the part of light to the collimating optical system. Exemplarylight-emitting elements that can be included in the light source includea red-light-emitting element, a green-light-emitting element, ablue-light-emitting element, and a white-light-emitting element. Thelight-emitting element may be a semiconductor laser element or an LED.The number of pixels included in the image forming device may bedetermined in accordance with the relevant specifications of the imagedisplay apparatus. For example, the number of pixels may be any of thefollowing: 320×240, 432×240, 640×480, 1024×768, and 1920×1080.

In the image display apparatus of the present application, the lightcollimated by the collimating optical system into a plurality ofdirectional rays in different traveling directions is made to beincident on the light-guiding plate. The light takes the form ofdirectional rays because it is important that optical wavefrontinformation at the time of incidence of such light on the light-guidingplate is retained even after the light is reflected by the first andsecond optical members and are output from the light-guiding plate.Specifically, a plurality of directional rays traveling in differentdirections can be generated by disposing the image forming device at adistance from the collimating optical system corresponding to the focallength of the collimating optical system. The collimating optical systemhas a function of converting information on the light emitted from theimage forming device from information indicating the positions of thepixels in the image forming device into information indicating theangles of the directional rays in the optical system of the opticaldevice. Further, since the collimating optical system collimates thelight emitted from the image forming device into a plurality ofdirectional rays traveling in different directions, the light receivedby the light-guiding plate in the form of plurality of directional raystraveling in different directions are output from the light-guidingplate after being propagated thereinside with total reflection. Thefirst optical member reflects or diffracts the directional rays receivedby the light-guiding plate so as to cause the directional rays to betotally reflected inside the light-guiding plate. The second opticalmember also reflects or diffracts the directional rays propagated withtotal reflection inside the light-guiding plate and causes thedirectional rays to emerge from the light-guiding plate.

In the image display apparatus of the present application, thelight-guiding plate has two surfaces (a first surface and a secondsurface) parallel to each other along, for example, the axis (the Y_(i)axis) of the light-guiding plate. Here, when a surface of thelight-guiding plate from which the light emerges is referred to as theplane of emergence, the first surface may include both the plane ofincidence and the plane of emergence. Alternatively, the first surfacemay include the plane of incidence and the second surface may includethe plane of emergence.

The first optical member is made of metal including alloy, for example,and can be configured as a reflective film (a kind of mirror) reflectingthe light received by the light-guiding plate, or a diffraction grating(such as a hologram diffraction grating film) diffracting the lightreceived by the light-guiding plate. The second optical member can beconfigured as a multilayer structure in which a number of dielectricfilms are stacked, a half mirror, a polarization beam splitter, or ahologram diffraction grating film. It is preferable that the first andsecond optical members be incorporated in, i.e., be provided inside, thelight-guiding plate. Alternatively, the first and second optical membersmay be fixed to the first and/or second surfaces of the light-guidingplate.

Exemplary materials for the light-guiding plate include the following:glass including optical glass such as fused quartz and BK7; and plasticmaterials including polymethylmethacrylate (PMMA), polycarbonate resin,acrylic resin, non-crystalline polypropylene resin, and styrenic resinsuch as acrylonitrile-styrene (AS) resin. The shape of the light-guidingplate is not limited to a flat shape, and may be a curved shape.

The collimating optical system included in the image display apparatusof the present application may be any of optical systems including oneof or a combination of a convex lens, a concave lens, afree-form-surface prism, and a hologram lens, as long as the opticalsystem generally has a positive optical power.

With the image display apparatus of the present application, an HMD canbe provided, for example, with a reduced weight and a reduced size.Accordingly, discomfort in wearing such an apparatus can be largelyreduced. Moreover, the manufacturing cost can be reduced.

Exemplary configurations of an image forming device or the light sourcehaving light-emitting elements and light valves include the following,other than a combination of a backlight generally emitting white lightand a liquid crystal display having red-light-emitting pixels,green-light-emitting pixels, and blue-light-emitting pixels.

(Image Forming Device A)

An image forming device A, which is a field-sequential color imageforming device, includes the following elements:

(α) a first image forming unit including a first light-emitting panel,the first light-emitting panel having first light-emitting elements thatemit blue light and are arranged in a two-dimensional matrix;

(β) a second image forming unit including a second light-emitting panel,the second light-emitting panel having second light-emitting elementsthat emit green light and are arranged in a two-dimensional matrix;

(γ) a third image forming unit including a third light-emitting panel,the third light-emitting panel having third light-emitting elements thatemit red light and are arranged in a two-dimensional matrix; and

(δ) means (a dichroic prism, for example, as in other image formingdevices described below) for integrating the light emitted from thefirst, second, and third image forming units into light propagatingalong a single optical path,

where the image forming device controls the individualemission/non-emission states of the first, second and thirdlight-emitting elements.

(Image Forming Device B)

An image forming device B, which is also a field-sequential color imageforming device, includes the following elements:

(α) a first image forming unit including a first light-emitting panelhaving first light-emitting elements that emit blue light and arearranged in a two-dimensional matrix, and a blue-light-transmissioncontroller (a light valve) controlling whether or not to allowtransmission of the light emitted from the first light-emitting panel;

(β) a second image forming unit including a second light-emitting panelhaving second light-emitting elements that emit green light and arearranged in a two-dimensional matrix, and a green-light-transmissioncontroller (a light valve) controlling whether or not to allowtransmission of the light emitted from the second light-emitting panel;

(γ) a third image forming unit including a third light-emitting panelhaving third light-emitting elements that emit red light and arearranged in a two-dimensional matrix, and a red-light-transmissioncontroller (a light valve) controlling whether or not to allowtransmission of the light emitted from the third light-emitting panel;and

(δ) means for integrating the light transmitted through the blue-,green-, and red-light-transmission controllers into light propagatingalong a single optical path,

where the image forming device displays an image by controlling with thelight-transmission controllers (light valves) whether or not to allowtransmission of the light emitted from the individual first, second, andthird light-emitting panels.

(Image Forming Device C)

An image forming device C, which is also a field-sequential color imageforming device, includes the following elements:

(α) a first image forming unit including a first light-emitting panelhaving first light-emitting elements that emit blue light and arearranged in a two-dimensional matrix;

(β) a second image forming unit including a second light-emitting panelhaving second light-emitting elements that emit green light and arearranged in a two-dimensional matrix;

(γ) a third image forming unit including a third light-emitting panelhaving third light-emitting elements that emit red light and arearranged in a two-dimensional matrix;

(δ) means for integrating the light emitted from the first, second, andthird image forming units into light propagating along a single opticalpath; and

(∈) a light-transmission controller (a light valve) controlling whetheror not to allow transmission of the light emitted from the means forintegrating the light along a single optical path,

where the image forming device displays an image by controlling with thelight-transmission controller whether or not to allow transmission ofthe light emitted from the light-emitting panels.

(Image Forming Device D)

An image forming device D, which is also a field-sequential color imageforming device, includes a light-transmission controller (a light valve)controlling whether or not to allow transmission of light emitted fromlight-emitting-element units arranged in a two-dimensional matrix. Theimage forming device D displays an image by controlling the individualemission/non-emission states of first light-emitting elements, secondlight-emitting elements, and third light-emitting elements included inthe respective light-emitting-element units in a time-shared manner andby controlling with the light-transmission controller whether or not toallow transmission of the light emitted from the individual first,second, and third light-emitting elements.

In the image display apparatus according to the first embodiment of thepresent application, a condition of θ₂>θ₁ is satisfied, and the opticalbaseline is not parallel to a normal to the light-guiding plate at theintersection of the optical baseline and the light-guiding plate. In theimage display apparatus according to the second embodiment of thepresent application, the light emitted from every pixel of the imageforming device and collimated by the collimating optical system into adirectional ray incident on the light-guiding plate is obliquely angledwith respect to the normal to the plane of incidence of thelight-guiding plate. Accordingly, the light emitted from the imageforming device, transmitted through the collimating optical system, andstriking the light-guiding plate is reflected by the light-guiding platein a direction away from the image forming device. Therefore, no ghostimage appears on the image forming device. Consequently, image contrastcan be improved and high-quality images can be displayed on the imageforming device.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a conceptual diagram of an image display apparatus of Example1;

FIGS. 2A and 2B schematically show the behavior of light emitted from animage forming device, transmitted through a collimating optical system,and striking a light-guiding plate, in the image display apparatus ofExample 1;

FIG. 3 is a conceptual diagram of an image display apparatus of Example2;

FIGS. 4A and 4B schematically show the behavior of light emitted from animage forming device, transmitted through a collimating optical system,and striking a light-guiding plate, in the image display apparatus ofExample 2;

FIG. 5 is a conceptual diagram of an image display apparatus of Example3;

FIG. 6 is a conceptual diagram of a modification of the image displayapparatus of Example 3;

FIG. 7 is a conceptual diagram showing an exemplary image forming devicesuitably modified for use in Examples;

FIG. 8 is a conceptual diagram showing a modification of the exemplaryimage forming device;

FIG. 9 is a conceptual diagram showing another modification of theexemplary image forming device;

FIG. 10 is a conceptual diagram showing another modification of theexemplary image forming device;

FIG. 11 is a conceptual diagram of a related-art image displayapparatus; and

FIG. 12 schematically shows the behavior of light emitted from an imageforming device, transmitted through a collimating optical system, andstriking a light-guiding plate, in the related-art image displayapparatus.

DETAILED DESCRIPTION

An embodiment of the present application will now be described withreference to specific examples, referring to the drawings.

Example 1

Example 1 relates to the image display apparatuses according to thefirst and second embodiments. FIG. 1 is a conceptual diagram of an imagedisplay apparatus 10 of Example 1. The image display apparatus 10includes the following elements:

(A) an image forming device 11 having a plurality of pixels arranged ina two-dimensional matrix;

(B) a collimating optical system 12 collimating light emitted from thepixels of the image forming device 11; and

(C) an optical device 20 receiving the light collimated by thecollimating optical system 12 into a plurality of directional rays indifferent traveling directions, guiding the light therethrough, andoutputting the light. The optical device 20 includes the followingelements:

(a) a light-guiding plate 21 propagating thereinside the light(specifically, the plurality of directional rays in different travelingdirections) received thereby with total reflection and outputting thepropagated light;

(b) a first optical member 30 reflecting (in Example 1) or diffractingthe light (the plurality of directional rays) received by thelight-guiding plate 21 so as to cause the light (the plurality ofdirectional rays) received by the light-guiding plate 21 to be totallyreflected inside the light-guiding plate 21; and

(c) a second optical member 40 causing the light (the plurality ofdirectional rays) propagated with total reflection inside thelight-guiding plate 21 to emerge (specifically, to emerge whilemaintaining the form of the plurality of directional rays) from thelight-guiding plate 21. The light that has emerged from thelight-guiding plate 21 travels toward and is incident on a pupil (theposition of a pupil) 13 of an observer (an image observer).

In Example 1, or in Examples 2 and 3 described below, the first opticalmember 30 is a reflective film (a kind of mirror) made of metal(specifically, aluminum) and is incorporated in the light-guiding plate21. Further, the second optical member 40 has a multilayer structureincluding a number of dielectric films and is incorporated in thelight-guiding plate 21. The dielectric films are composed as films ofTiO₂ as a high-dielectric-constant material and SiO₂ as alow-dielectric-constant material, for example. An exemplary multilayerstructure in which a number of dielectric films are stacked is disclosedin Japanese Unexamined Patent Application Publication (Translation ofPCT Application) No. 2005-521099. Although the second optical member 40shown in the drawings is a member including six layers of dielectricfilms, the second optical member 40 is not limited thereto. There areprovided thin pieces composed of the same material as that of thelight-guiding plate 21 between the dielectric films.

The first optical member 30 can be obtained in the following manner: Aportion 24 of the light-guiding plate 21 that is to be the base of thefirst optical member 30 is cut off into a shape having a sloping surfaceon which the first optical member 30 is to be provided. Then, after areflective film is formed on the sloping surface by vacuum deposition,the portion 24 is bonded back to the light-guiding plate 21. The secondoptical member 40 can be obtained in the following manner: First, amultilayer structure in which thin pieces made of the same material asthat of the light-guiding plate 21 (glass, for example) and dielectricfilms (obtained by vacuum deposition, for example) are alternatelystacked is manufactured. A portion 25 of the light-guiding plate 21 atwhich the second optical member 40 is to be provided is cut off into ashape having a sloping surface. Then, after the multilayer structure isbonded onto the sloping surface, the outer shape of the resultingstructure is adjusted by polishing or the like. Thus, the optical device20 in which the first optical member 30 and the second optical member 40are incorporated can be obtained.

In Example 1, or in Example 2 described below, the image forming device11 includes a reflective spatial light modulator 50 and a light source53 having a light-emitting diode that emits white light. Morespecifically, the reflective spatial light modulator 50 includes aliquid crystal display (LCD) 51 that is of an LCOS device serving as alight valve, and a polarization beam splitter 52 that reflects part ofthe light emitted from the light source 53 and guides the part of thelight to the liquid crystal display 51 while transmitting part of thelight reflected by the liquid crystal display 51 and guiding the part ofthe light to the collimating optical system 12. The polarization beamsplitter 52 has the same configuration as those of related-artpolarization beam splitters. The light emitted as unpolarized light fromthe light source 53 strikes the polarization beam splitter 52. Thepolarization beam splitter 52 transmits and outputs p-polarizedcomponents to the outside of its system, whereas the polarization beamsplitter 52 reflects s-polarized components. The reflected s-polarizedcomponents enter the liquid crystal display 51, are reflectedthereinside, and are output to the outside thereof. Among the light thatis output from the liquid crystal display 51, light that is output frompixels displaying “white” contain a relatively large number ofp-polarized components, and light that is output from pixels displaying“black” contain a relatively large number of s-polarized components.That is, among the light that strikes the polarization beam splitter 52after being output from the liquid crystal display 51, p-polarizedcomponents are transmitted through the polarization beam splitter 52 andare guided toward the collimating optical system 12, while s-polarizedcomponents are reflected by the polarization beam splitter 52 and arefed back to the light source 53. The liquid crystal display 51 includesa plurality of pixels (J pixels per row along the Y_(i) axis and Kpixels per column along the Z_(i) axis: J×K=320×240 pixels, for example,with the number of liquid crystal cells being three times larger thanthe number of pixels) that are arranged in a pattern such as atwo-dimensional matrix. The collimating optical system 12 is a convexlens, for example. The image forming device 11 (more specifically, theliquid crystal display 51) is positioned at a distance from thecollimating optical system 12 corresponding to the focal length of thecollimating optical system 12 so that a plurality of directional rays indifferent traveling directions are generated by the collimating opticalsystem 12. A single pixel includes a red-light-emitting subpixel thatemits red light, a green-light-emitting subpixel that emits green light,and a blue-light-emitting subpixel that emits blue light.

In Example 1, or in Examples 2 and 3 described below, the light-guidingplate 21 has two surfaces (a first surface 22 and a second surface 23)parallel to each other along the axis of the light-guiding plate 21. TheX_(i) axis is a normal to the plane of incidence of the light-guidingplate 21 that extends through the origin (O_(i)) defined at the centerof the first optical member 30 and takes positive values in a directiontoward the collimating optical system 12. The first surface 22 and thesecond surface 23 are positioned opposite each other. The light, in theform of directional rays, enters the light-guiding plate 21 through thefirst surface 22, serving as the plane of incidence, is propagated withtotal reflection inside the light-guiding plate 21, and emerges throughthe first surface 22, serving as the plane of emergence. Anotherconfiguration may be employed. For example, the second surface 23 mayserve as the plane of incidence, and the first surface 22 may serve asthe plane of emergence.

FIGS. 2A and 2B each schematically show the behavior of light emittedfrom the image forming device 11, transmitted through the collimatingoptical system 12, and striking the light-guiding plate 21. In the imagedisplay apparatus 10 of Example 1, referring to FIGS. 2A and 2B, a lightray emitted from a pixel located farthest from the center of the imageforming device 11 and passing through the front nodal point of thecollimating optical system 12 is incident on the collimating opticalsystem 12 at an angle θ₁, and a light ray emitted from the pixel locatedat the center of the image forming device 11 and passing through thefront nodal point of the collimating optical system 12 (the center lightray CL) is incident on the light-guiding plate 21 at an angle θ₂. Here,a condition of θ₂>θ₁ is satisfied. In Example 1, or in Examples 2 and 3described below, it is defined that the light ray emitted from the pixellocated farthest along an axis corresponding to the Y_(i) axis from thecenter of the image forming device 11 and passing through the frontnodal point of the collimating optical system 12 is incident on thecollimating optical system 12 at an angle of θ₁, and that the centerlight ray CL emitted from the pixel located at the center of the imageforming device 11 and passing through the front nodal point of thecollimating optical system 12 is incident on the light-guiding plate 21at an angle of θ₂. Other definitions (settings) of these angles θ₁ andθ₂ may be employed. Further, in the image display apparatus 10 ofExample 1, an optical baseline OBL optically extending through thecenter of the image forming device 11 and the front nodal point of thecollimating optical system 12 is not parallel to a normal (shown in thetwo-dot chain line NL) to the light-guiding plate 21 at the intersectionof the optical baseline OBL and the plane of incidence of thelight-guiding plate 21. That is, the optical baseline OBL and the normalNL form a predetermined angle therebetween. Therefore, the light rayemitted from the pixel located farthest from the center of the imageforming device 11, passing through the collimating optical system 12,and striking the light-guiding plate 21 is reflected by thelight-guiding plate 21 in a direction away from the image forming device11. In short, the angle formed between the optical baseline OBL and thenormal NL is set in such a manner that the light emitted from the pixellocated farthest from the center of the image forming device 11, passingthrough the collimating optical system 12, and striking thelight-guiding plate 21 is reflected by the light-guiding plate 21 in adirection away from the image forming device 11. For reference, FIG. 2Ashows a case of θ₂=θ₁, and FIG. 2B shows a case of θ₂>θ₁. Further, inthe image display apparatus 10 of Example 1, the light emitted fromevery pixel of the image forming device 11 and collimated by thecollimating optical system 12 into a directional ray incident on thelight-guiding plate is not parallel to the normal to the plane ofincidence (the first surface 22) of the light-guiding plate 21.Furthermore, the light emitted from every pixel of the image formingdevice 11 and collimated by the collimating optical system 12 into adirectional ray has a portion thereof reflected, if any, at the plane ofincidence (the first surface 22) of the light-guiding plate 21 in adirection in which the portion of the directional ray is not incident onthe image forming device 11.

Specifically, the following settings are made in Example 1:

θ₁=8 degrees

θ₂=10 degrees

In the image display apparatus 10 of Example 1, a near-end-pixel rayLt_(PX) and the Y_(i) axis form an acute angle therebetween. Thenear-end-pixel ray Lt_(PX) denotes the light ray that is emitted fromthe pixel located farthest from the center of the image forming device11, or the center of the liquid crystal display 51 in Example 1, (i.e.,in Example 1, the pixel located on an axis corresponding to the Y_(i)axis farthest from the center of the image forming device 11) and nearto the second optical member 40 and, at the same time, passes throughthe front nodal point of the collimating optical system 12.Specifically, the aforementioned acute angle is expressed as[90−(θ₂+θ₁)] degrees. The center light ray CL is optically parallel toan X_(i)Y_(i) plane while intersecting an X_(i)Z_(i) plane at the angleθ₂. That is, the center light ray CL is incident on the light-guidingplate 21 at an acute angle from a side near to the second optical member40. In Example 1, or in Examples 2 and 3 described below, thenear-side-pixel ray Lt_(PX), the center light ray CL, and afar-end-pixel ray Lt_(FH) described below, are contained in theX_(i)Y_(i) plane. In another case, however, the near-side-pixel rayLt_(PX), the center light ray CL, and the far-end-pixel ray Lt_(FH) maybe not contained in the X_(i)Y_(i) plane. In the latter case, the anglesθ₁ and θ₂ may be treated as solid angles.

In Example 1, or in Example 2 described below, the optical axis of thecollimating optical system 12 optically extends through the center ofthe image forming device 11. In Example 1, the center of the imageforming device 11, or the center of the liquid crystal display 51, lieson the extension of the optical axis of the collimating optical system12. Another configuration may be employed. For example, the optical axisof the collimating optical system 12 may optically extend through thecenter of the image forming device 11, or the center of the liquidcrystal display 51, via other optical systems, or the light propagatedalong the optical axis of the collimating optical system 12 may beincident from the collimating optical system 12 either directly on thelight-guiding plate 21 or via other optical systems.

The observer may wear two image display apparatuses as a pair, one forthe right eye and the other for the left eye, or may wear a single imagedisplay apparatus on one eye. In the case where two image displayapparatuses are worn, both image display apparatuses for the right andleft eyes may display the same image or may display different images(for example, images that can be composed into a three-dimensionalimage). In such cases, each image display apparatus functions as an HMD.

The light, in the form of directional rays, that has entered thelight-guiding plate 21 and has struck the first optical member 30 isreflected by the first optical member 30 and is propagated with totalreflection inside the light-guiding plate 21. The state of propagationof the directional light in the light-guiding plate 21 varies withpositions on the image forming device 11 from which the light isemitted. For example, as shown in FIGS. 2A and 2B, the angle ofincidence (θ_(PX)) of the near-end-pixel ray Lt_(PX) on thelight-guiding plate 21 is larger than the angle of incidence (θ_(FH)) ofthe far-end-pixel ray Lt_(FH) on the light-guiding plate 21. Thefar-end-pixel ray Lt_(FH) denotes the ray that is emitted from the pixellocated farthest from the center of the image forming device 11, or thecenter of the liquid crystal display 51 in Example 1, (i.e., in Example1, the pixel located on an axis corresponding to the Y_(i) axis farthestfrom the center of the image forming device 11) and away from the secondoptical member 40 and, at the same time, passes through the front nodalpoint of the collimating optical system 12. Accordingly, the angle oftotal reflection of the near-end-pixel ray Lt_(PX) occurring in thelight-guiding plate 21 is smaller than that of the total reflection ofthe far-end-pixel ray Lt_(FH) occurring in the light-guiding plate 21.The angle of total reflection of the center light ray CL occurring inthe light-guiding plate 21 is an intermediate value between theforegoing two.

The second optical member 40 has a multilayer structure in which anumber of dielectric films are stacked. Whether the light propagatedinside the light-guiding plate 21 and striking the dielectric films istransmitted through the dielectric films or is reflected by thedielectric films and is output to the outside of the light-guiding plate21 is determined by the angle at which the light strikes the dielectricfilms. Thus, the light emitted from the second optical member 40 reachesthe pupil 13 of the observer, whereby the light can be recognized as animage. Moreover, with such a configuration, the thickness of thelight-guiding plate 21 can be reduced.

In the image display apparatus 10 of Example 1, the condition of θ₂>θ₁is satisfied, and the optical baseline OBL is not parallel to the normalto the light-guiding plate 21 extending from the intersection of theoptical baseline OBL and the light-guiding plate 21. Specifically, theoptical baseline OBL and the normal form the angle θ₂ therebetween.Further, the light emitted from every pixel of the image forming device11 and collimated by the collimating optical system 12 into adirectional ray incident on the light-guiding plate 21 is not parallelto the normal to the plane of incidence (the first surface 22) of thelight-guiding plate 21. This means that every ray (for example, thefar-end-pixel ray Lt_(FH)) emitted from the image forming device 11,collimated by the collimating optical system 12, and striking thelight-guiding plate 21 is reflected, if any, at the plane of incidence(the first surface 22) of the light-guiding plate 21 in a direction awayfrom the image forming device 11. Therefore, no ghost image is formed onthe image forming device 11. Consequently, image contrast can beimproved and high-quality images can be displayed on the image formingdevice 11.

Example 2

Example 2 is a modification of Example 1. FIG. 3 is a conceptual diagramof an image display apparatus 110 of Example 2. FIGS. 4A and 4B eachschematically show the behavior of light emitted from the image formingdevice 11, transmitted through the collimating optical system 12, andstriking the light-guiding plate 21. The image display apparatus 110 ofExample 2 also satisfies the condition of θ₂>θ₁. For reference, FIG. 4Ashows a case of θ₂=θ₁, and FIG. 4B shows a case of θ₂>θ₁. The angles θ₁and θ₂ in Example 2 are set to the same values as those in Example 1.However, in the image display apparatus 110 of Example 2, thefar-end-pixel ray Lt_(FH) and the Y_(i) axis intersects at an obtuseangle. Specifically, this obtuse angle is expressed as [90+(θ₂−θ₁)]degrees. The center light ray CL is optically parallel to the X_(i)Y_(i)plane while intersecting the X_(i)Z_(i) plane at the angle θ₂. That is,the center light ray CL is incident on the light-guiding plate 21 at anobtuse angle from a side away from the second optical member 40.

The image display apparatus 110 of Example 2 can be configured in thesame manner as in the case of the image display apparatus 10 of Example1, except the arrangement of the image forming device described above.Hence, detailed description of the image display apparatus 110 will beomitted.

Also in the image display apparatus 110 of Example 2, the condition ofθ₂>θ₁ is satisfied, and the optical baseline OBL is not parallel to thenormal to the light-guiding plate 21 extending from the intersection ofthe optical baseline OBL and the light-guiding plate 21. Specifically,the optical baseline OBL and the normal form the angle θ₂ therebetween.Further, the light emitted from every pixel of the image forming device11 and collimated by the collimating optical system 12 into adirectional ray incident on the light-guiding plate 21 is not parallelto the normal to the plane of incidence (the first surface 22) of thelight-guiding plate 21. This means that every ray (for example, thenear-end-pixel ray Lt_(PX)) emitted from the image forming device 11,collimated by the collimating optical system 12, and striking thelight-guiding plate 21 is reflected, if any, at the plane of incidence(the first surface 22) of the light-guiding plate 21 in a direction awayfrom the image forming device 11. Therefore, no ghost image is formed onthe image forming device 11. Consequently, image contrast can beimproved and high-quality images can be displayed on the image formingdevice 11.

Example 3

Example 3 is a modification of Example 1 or Example 2. FIGS. 5 and 6 areconceptual diagrams of an image display apparatus 210 of Example 3,showing modifications of Example 1 and Example 2, respectively. In theimage display apparatus 210 shown in FIGS. 5 and 6, the optical axis ofa collimating optical system 212 is parallel to the X_(i) axis. Theoptical axis of the collimating optical system 212 optically extendsthrough a point away from the center of an image forming device 211, orthe center of a liquid crystal display 251. With such a configuration,the center light ray CL is made to be optically parallel to theX_(i)Y_(i) plane while intersecting the X_(i)Z_(i) plane at an acute orobtuse angle. Specifically, the angles θ₁ and θ₂ in Example 3 are set tothe same values as those in Example 1 or 2. The liquid crystal display251 of Example 3 is a transmissive liquid crystal display.

The image display apparatus 210 of Example 3 can be configured in thesame manner as in the case of the image display apparatus of Example 1or 2, except the arrangement described above. Hence, detaileddescription of the image display apparatus 210 will be omitted.

While the present application has been described on the basis ofpreferred examples, the present application is not limited thereto. Theconfigurations of the image display apparatuses described above are onlyexemplary, and appropriate modifications can be made thereto.

FIG. 7 is a conceptual diagram of another exemplary image forming devicemodified so as to be suitable for use in Examples described above. Thisimage forming device includes a light-emitting panel havinglight-emitting elements 301, which are semiconductor light-emittingelements, arranged in a two-dimensional matrix. The image forming deviceserves as an active matrix image forming device, which displays an imageby controlling the individual emission/non-emission states of thelight-emitting elements 301 and having the observer directly observe theemission states of the light-emitting elements 301. The light emittedfrom this image forming device is transmitted through the collimatingoptical system 12 or 212 and is incident on the light-guiding plate 21.

FIG. 8 is a conceptual diagram of a color image forming device, anotherexemplary modification, including the following elements:

(α) a red-light-emitting panel 311R having red-light-emitting elements301R that emit red light and are arranged in a two-dimensional matrix;

(β) a green-light-emitting panel 311G having green-light-emittingelements 301G that emit green light and are arranged in atwo-dimensional matrix;

(γ) a blue-light-emitting panel 311B having blue-light-emitting elements301B that emit blue light and are arranged in a two-dimensional matrix;and

(δ) means (a dichroic prism 303, for example) for integrating the lightemitted from the red-light-emitting panel 311R, the green-light-emittingpanel 311G, and the blue-light-emitting panel 311B into lightpropagating along a single optical path,

where the color image forming device controls the individualemission/non-emission states of the red-light-emitting elements 301R,the green-light-emitting elements 301G, and the blue-light-emittingelements 301B. The light emitted from this image forming device is alsotransmitted through the collimating optical system 12 or 212 and isincident on the light-guiding plate 21. The image forming device alsoincludes microlenses 312 that collect the light emitted from thelight-emitting elements.

FIG. 9 is a conceptual diagram of another image forming device includingthe light-emitting panels 311R, 311G, and 311B having the light-emittingelements 301R, 301G, and 301B, respectively, arranged in atwo-dimensional matrix, and so forth. The light emitted from thelight-emitting panels 311R, 311G, and 311B is controlled by lighttransmission controllers 304R, 304G, and 304B to be transmittedtherethrough or to be blocked thereby. The light transmitted through thelight transmission controllers 304R, 304G, and 304B enters the dichroicprism 303, is integrated into light propagating along a single opticalpath, is transmitted through the collimating optical system 12 or 212,and is incident on the light-guiding plate 21.

FIG. 10 is a conceptual diagram of another image forming deviceincluding the light-emitting panels 311R, 311G, and 311B having thelight-emitting elements 301R, 301G, and 301B, respectively, arranged ina two-dimensional matrix, and so forth. The light emitted from thelight-emitting panels 311R, 311G, and 311B enters the dichroic prism 303and is integrated into light propagating along a single optical path.The integrated light output from the dichroic prism 303 is controlled bya light transmission controller 304 to be transmitted therethrough or tobe blocked thereby. The light transmitted through the light transmissioncontroller 304 is further transmitted through the collimating opticalsystem 12 or 212 and is incident on the light-guiding plate 21.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. An image display apparatus comprising: an image forming device havinga plurality of pixels; a collimating optical system; and an opticaldevice configured to receive light, guide the light therethrough, andoutput the light, wherein, when light emitted from a pixel locatedfarthest from a center of the image forming device and passing through anodal point of the collimating optical system near to the image formingdevice is incident on the collimating optical system at an angle of θ₁,and when light emitted from a pixel located at the center of the imageforming device and passing through the nodal point of the collimatingoptical system near to the image forming device is incident on thelight-guiding plate at an angle of θ₂, a condition of θ₂>θ₁ issatisfied.
 2. The image display apparatus according to claim 1, whereinthe image forming device includes a reflective spatial light modulatorand a light source.
 3. The image display apparatus according to claim 2,wherein the reflective spatial light modulator includes a liquid crystaldisplay and a polarization beam splitter, the polarization beam splitterreflecting a part of light emitted from the light source and guiding thepart of light to the liquid crystal display while transmitting the partof light reflected by the liquid crystal display and guiding the part oflight to the collimating optical system.
 4. A head-mounted displaycomprising: an image forming device having a plurality of pixels; acollimating optical system; and an optical device configured to receivelight, guide the light therethrough, and output the light, wherein, whenlight emitted from a pixel located farthest from a center of the imageforming device and passing through a nodal point of the collimatingoptical system near to the image forming device is incident on thecollimating optical system at an angle of θ₁, and when light emittedfrom a pixel located at the center of the image forming device andpassing through the nodal point of the collimating optical system nearto the image forming device is incident on the light-guiding plate at anangle of θ₂, a condition of θ₂>θ₁ is satisfied.